code: def test_isotonic_regression(self):
      data = np.abs(np.random.randn(100))
      data = data.cumsum()
      df = pdml.ModelFrame(np.arange(len(data)), target=data)
  
      result = df.isotonic.isotonic_regression()
      expected = isotonic.isotonic_regression(data)
      self.assertIsInstance(result, pdml.ModelSeries)
      tm.assert_index_equal(result.index, df.index)
      tm.assert_numpy_array_equal(result.values, expected)
  
file_path: pandas-ml/pandas_ml/skaccessors/test/test_isotonic.py
imports: import numpy
  import sklearn.isotonic
  import pandas_ml
  import pandas_ml.util.testing
label_desc: Use image node_id 2 for calling the TestIsotonic obj's underlying member method code with example usage: obj.test_isotonic_regression() without return types